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Fixing the 550 5.7.1 [FBL] error

If you receive a bounce message with this error, it's because an email recipient has directly complained about email originating from your IP address or account. In keeping with email sender best practices, MailChannels automatically blocks senders who receive complaints.

We unfortunately cannot reveal who complained about your email. To do so would enable spammers to fine tune or "wash" their recipient lists to avoid future detection. Complaints originate from email users on popular email services, including:

  • Microsoft® Live Hotmail
  • Gmail
  • AOL Mail
  • ... and others

What caused the error?

If you receive this type of rejection from us, it's possible you did nothing wrong. Email recipients frequently complain about legitimate messages. Sometimes it may seem easier to hit the "spam" button than the "delete" button. However, there are some things you can do to improve your chances of staying on the good side of your recipients, including:

  • Only sending email messages that recipients could reasonably expect to receive;
  • Not surprising recipients with new messages after many months of zero contact;
  • Keeping the purpose of your communication as clear as possible; and,
  • Providing unsubscribe links prominently at the top AND bottom of each message.

The M3AAWG Sender Best Common Practices document is an excellent resource and gives an overview of the current best common practices for sending commercial electronic messaging,

How long will I be blocked?

Our system uses an adaptive approach for blocking senders that receive complaints. Once the level of complaints drops back to an acceptable level, the sender will no longer be blocked. Unfortunately we do not generally accept requests to expedite the unblocking of a sender who has been blocked due to complaints.

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  • Avatar
    Geoffrey Yates

    This is very very bad. I got blocked and I checked my log. I have never sent SPAM. The log is clear. All the email that I see in the log I can recognize. 100% not SPAM. Very disappointed

  • Avatar
    Ken Simpson

    Geoffrey, please submit a support request if you have questions about being blocked. Our team responds 24x7x365.

  • Avatar
    Geoffrey Yates

    I did that: Got this reply:
    FBL indicates that feedback loop complaints (receivers complaining about mails you have sent) against the mails sent from your accounts. Hence, the mails from your accounts were temporarily blocked.

    This is an automated block and if we do not see any more complaints, your account will be automatically allowed to send mails within 24 hours. We do not whitelist any senders against whom there are FBL complaints

    We will check our system logs and will provide you the details of the exact FBL complaints.


    I'm waiting now. VERY VERY DISAPPOINTING. 24h?????? for not sending one SPAM email???????

  • Avatar
    Ken Simpson

    Geoffrey, thanks for investigating. FBLs are generated by email recipients when they click the "report spam" button. Unfortunately, we can't know why people sometimes flag email as spam; however, we do know that receiving systems such as AOL, Yahoo!, and others, use these reports to train their spam filters. Are you sending to a mailing list, or just sending one off emails?

  • Avatar
    Geoffrey Yates

    OK, I received the explanation. It seams that my system is compromise. I asked my webhosting to investigate and see what the problem is. I will come back and post what they find. I have no idea how they got in. Now I look like a n00b.

  • Avatar
    Ken Simpson

    Oh, sorry to hear that. Glad you will be getting some help.

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